The present invention relates to a binary circuit where image signal outputted from an image sensor is converted into a binary signal.
In the prior art, binary circuits to obtain an image signal using an image sensor and to convert the image signal into a binary signal have been used in may fields. FIG. 1 is a block diagram illustrating a binary circuit in the prior art. In FIG. 1, numeral 1 designates an image pick-up element for converting optical information into electric signals, e.g., a one-dimensional image sensor, and numeral 2 designates a circuit for generating drive clocks of fixed frequency to read the light receiving signal in sequence from the image sensor 1. The image sensor 1 outputs image signals in synchronization with clocks from the drive clock generator 2. Numeral 3 designates an amplifier for amplifying the image signals, and numeral 5 designates a reference voltage generator for generating reference voltage to discriminate level of white or black of the image signals. A variable resistor 6 adjusts and determines the reference voltage. A comparator 4 compares the reference voltage and the image signal, and generates a binary signal. The comparator 4 serves to emphasize the dark and pale state of the original picture by utilizing the binary signal. In a circuit of the prior art, for example, disclosed in Japanese patent application laid-open (Kokai) No. 60-158769, the reference voltage to convert the image signal of the dark and pale state into binary signal is adjusted using the variable resistor 6.
In such constitution of the prior art, the semi-fixed resistor 6 for adjusting the reference voltage must be arranged at position to make the adjustment easy and a method to facilitate the adjustment must be considered, resulting in the limitation that the circuit can not be made into a compact and simple structure.
Also in a color image signal binary circuit where optical information being indicent to an image sensor is color image, there exists a similar problem and adjustment of the reference voltage corresponding to color component image signals of plural colors is further complicated.